Process for manufacturing of composite pipes

Abstract

Improved composite pipes are proposed which comprise an outer pipe made of plastic and a thin lead layer on the inner wall of the outer pipe. The lead layer is formed by arranging a lead pipe in the outer pipe and expanding it by use of pressure medium into close contact with the inner wall of the outer pipe. The outer pipe may be circular or square or double-path. A process for producing the composite pipes is also proposed.

What we claim: 
     
       1. A process for producing a composite pipe comprising steps of arranging a lead pipe in an outer pipe made of plastic with some gap therebetween, and expanding the lead pipe by sealing a pressure medium in said lead pipe until it gets into close contact with the inner wall of said outer pipe to form a lead layer. 
     
     
       2. A process as claim in claim 1, wherein said lead pipe is arranged in said outer pipe by forming said lead pipe and said outer pipe separately and inserting said lead pipe into said outer pipe. 
     
     
       3. A process as claimed in claim 1, wherein said lead pipe is arranged in said outer pipe by forming a lead pipe, feeding said lead pipe to a continuous extruder, and extruding said outer pipe thereby while enclosing said lead pipe as a core. 
     
     
       4. A process as claimed in claim 1, wherein both of said outer pipe and said lead pipe are formed by a continuous extrusion. 
     
     
       5. A process as claimed in claim 1, wherein the thickness of said lead pipe prior to expansion is not less than 2 mm. 
     
     
       6. A process as claimed in claim 1, wherein the thickness of said lead layer is not more than 1 mm. 
     
     
       7. A process as claimed in claim 1, wherein said lead pipe is heated to a temperature not higher than 150° C. before expanding it. 
     
     
       8. A process for producing a composite pipe comprising steps of arranging a lead pipe in an outer pipe made of plastic with some gap therebetween, and expanding the lead pipe when inserted into the outer pipe until said lead pipe expands into close contact with the inner wall of said outer pipe to form a lead layer thereupon. 
     
     
       9. A process as claimed in claim 8, wherein said lead pipe is arranged in said outer pipe by forming said lead pipe and said outer pipe separately and inserting said lead pipe into said outer pipe. 
     
     
       10. A process as claimed in claim 8, wherein said lead pipe is arranged in said outer pipe by forming a lead pipe, feeding said lead pipe to a continuous extruder, and extruding said outer pipe thereby while enclosing said lead pipe as a core. 
     
     
       11. A process as claimed in claim 8, wherein both of said outer pipe and said lead pipe are formed by a continuous extrusion. 
     
     
       12. A process as claimed in claim 8 wherein the thickness of said lead pipe prior to expansion is not less than 2 mm. 
     
     
       13. A process as claimed in claim 8, wherein the thickness of said lead layer is not more than 1 mm. 
     
     
       14. A process as claimed in claim 8 wherein said lead pipe is heated to a temperature not higher than 150° C. before expanding it.